Among thermoplastic elastomers, styrene-based thermoplastic elastomers such as a styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene-styrene block copolymer (SIS), and hydrogenated products thereof are widely used from the viewpoints of excellent flexibility, rubber elasticity, recyclability, and the like with low cost.
Studies have been conducted so as to improve various physical properties of the styrene-based thermoplastic elastomers. For example, a thermoplastic elastomer resin composition for molding powder, which is used so as to obtain a molded article with soft texture and excellent scratch resistance, and includes a styrene-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, and the like (see PTL 1); and a composition having excellent flexibility, mold processability, and scratch resistance, which is a thermoplastic elastomer composition obtained by adding a copolymer having units exhibiting compatibility with both of a styrene-based thermoplastic elastomer (a hydrogenated block copolymer) and a methacryl-based resin to a composition including both (see PTL 2) have been proposed.
Furthermore, there have been proposed a thermoplastic resin composition retaining surface characteristics such as surface hardness exhibited by an acryl-based resin, weather resistance, transparency, and the like, and also having properties such as flexibility and low-temperature characteristics, which is an acryl-based thermoplastic resin composition obtained by blending a hydrogenated product of a block copolymer including a polymer block (a) containing an aromatic vinyl compound having a specific molecular weight, and a polymer block (b) containing isoprene, or isoprene and butadiene, with an acryl-based resin having a specific intrinsic viscosity at a specific ratio (see PTL 3); and a thermoplastic resin composition having a block containing an a-b-a structure (a: a block containing aromatic vinyl monomers and b: a block containing isoprene and/or butadiene) with respect to an acryl-based resin, and containing a hydrogenated product of 3-component block copolymers having a specific number average molecular weight at a specific ratio (see PTL 4).
There has been proposed a composition having superior flexibility, weather resistance, and good appearance characteristics, which is a thermoplastic resin composition including a polyolefin-based resin (A), a hydrogenated product (B) of a thermoplastic block copolymer consisting of a block containing aromatic vinyl monomers and a block containing isoprene and/or butadiene, an acryl-based resin (C), a hydrocarbon-based softening agent (D), and a hydrogenated product (E) of a thermoplastic block copolymer consisting of a block containing aromatic vinyl monomers and a block containing isoprene and/or butadiene, having a polymerized product of an acryl-based monomer in a side chain thereof (see PTL 5).
The composition of PTL 1 has been tentatively improved due to its inferiority to a polyurethane-based thermoplastic elastomer with respect to scratch resistance, but it still has problems such as deteriorated performance and yellowing in a case of being formed into a molded article from the viewpoints of insufficient hydrolysis resistance and weather resistance. The compositions of PTLs 2 to 5 retain surface characteristics such as surface hardness exhibited by an acryl-based resin, weather resistance, transparency, and the like, and also have excellent properties of mold processability, transparency, and the like due to their sufficient flexibility. However, the scratch resistance and the abrasion resistance of the compositions were evaluated, and as a result, they are not sufficiently satisfactory.
Under these circumstances, there remains a demand for a thermoplastic polymer composition which can be effectively used in sites where the composition is subjected to frequent friction and applications where aesthetic appearance is important, for example.
In order to solve the above problems, PTL 6 proposes the following polymer composition.
A polymer composition including:
a block copolymer (a) with a weight average molecular weight of 30,000 to 200,000, which has a polymer block A mainly composed of α-methylstyrene and a polymer block B which may be hydrogenated, containing a conjugated diene or isobutylene, an acryl-based resin (b), and a softening agent (c), at a blending ratio (mass ratio) satisfying the following formulae (1) and (2):0.05≦Wb/Wa≦2  (1)Wc/(Wa+Wb+Wc)≦0.5  (2)
wherein Wa, Wb, and Wc represent the contents (by mass) of the respective components of the block copolymer (a), the acryl-based resin (b), and the softening agent (c), each of which constitutes the polymer composition.